Carrier aggregation, in which a wireless communications device simultaneously transmits and/or receives radio frequency (RF) signals over multiple frequency bands, has become increasingly popular in order to maximize data throughput. Supporting carrier aggregation in a wireless communications device presents several challenges in the design and manufacture of the device. FIG. 1 is a functional schematic of conventional radio frequency (RF) front end circuitry 10 suitable for performing both uplink carrier aggregation in which multiple RF transmit signals in different operating bands are simultaneously transmitted and downlink carrier aggregation in which multiple RF receive signals in different operating bands are simultaneously received. The conventional RF front end circuitry 10 includes primary communications circuitry 12, secondary communications circuitry 14, and control circuitry 16. The primary communications circuitry 12 is coupled to a primary antenna 18. The secondary communications circuitry 14 is coupled to a secondary antenna 20. The control circuitry 16 is coupled to both the primary communications circuitry 12 and the secondary communications circuitry 14.
The primary communications circuitry 12 includes primary front end switching circuitry 22, primary RF filtering circuitry 24, and a number of RF power amplifiers 26. The primary front end switching circuitry 22 is coupled between the primary RF filtering circuitry 24 and a primary antenna node 28, which is in turn coupled to the primary antenna 18. The primary RF filtering circuitry 24 includes a primary filter 30 coupled between a common node 32 and a number of input/output nodes 34. An output of a first one of the RF power amplifiers 26A is coupled to a third one of the input/output nodes 34C. An output of a second one of the RF power amplifiers 26B is coupled to a first one of the input/output nodes 34A. The primary front end switching circuitry 22 includes a first primary front end switching element SW_PFE1 coupled between the primary antenna node 28 and the common node 32 and a second primary front end switching element SW_PFE2 coupled between the primary antenna node 28 and an additional filter node 36, which is configured to be coupled to an additional filter (not shown to simplify the drawings and present description). While not shown, additional switch throws to route to additional filters may be included in the primary front end switching circuitry 22 for supporting transmission and reception in additional RF bands.
The primary filter 30 is configured to pass RF signals within a transmit portion of a first operating band between the first one of the input/output nodes 34A and the common node 32 while attenuating signals outside of the transmit portion of the first operating band between the first one of the input/output nodes 34A and the common node 32, pass RF signals within a receive portion of the first operating band between the common node 32 and a second one of the input/output nodes 34B while attenuating signals outside the receive portion of the first operating band between the common node 32 and the second one of the input/output nodes 34B, pass RF signals within a transmit portion of a second operating band between the third one of the input/output nodes 34C and the common node 32 while attenuating signals outside of the receive portion of the second operating band between the third one of the input/output nodes 34C and the common node 32, and pass RF signals within a receive portion of the second operating band between the common node 32 and a fourth one of the input/output nodes 34D while attenuating signals outside the receive portion of the second operating band between the common node 32 and the fourth one of the input/output nodes 34D. Those skilled in the art will appreciate that the primary RF filtering circuitry 24 enables the conventional RF front end circuitry 10 to simultaneously transmit and receive RF signals within the first operating band and the second operating band.
The first one of the RF power amplifiers 26A is configured to receive and amplify RF transmit signals within the transmit portion of the first operating band. The second one of the RF power amplifiers 26B is configured to receive and amplify RF transmit signals within the transmit portion of the second operating band.
The primary front end switching circuitry 22 is configured to couple a number of filters in the primary RF filtering circuitry 24 to the primary antenna node 28 in order to selectively route RF signals to the appropriate signal paths in the conventional RF front end circuitry 10.
While not shown, a number of low-noise amplifiers (LNAs) may connect to the second one of the input/output nodes 34B and the fourth one of the input/output nodes 34D in order to amplify the receive signals therefrom for further processing.
The secondary communications circuitry 14 includes secondary front end switching circuitry 38 and secondary RF filtering circuitry 40. The secondary front end switching circuitry 38 is coupled between the secondary RF filtering circuitry 40 and a secondary antenna node 42, which is in turn coupled to the secondary antenna 20. The secondary RF filtering circuitry 40 includes a secondary filter 44 coupled between a common node 46 and a number of input/output nodes 48. The secondary front end switching circuitry 38 includes a first secondary front end switching element SW_SFE1 coupled between the secondary antenna node 42 and the common node 46 and a second secondary front end switching element SW_SFE2 coupled between the secondary antenna node 42 and an additional filter node 50, which is configured to be coupled to an additional filter (not shown to simplify the drawings and present description). While not shown, additional switch throws to route to additional filters may be included in the secondary front end switching circuitry 38 for supporting reception in additional RF bands.
The secondary filter 44 is configured to pass RF signals within the receive portion of the first operating band between the common node 46 and a first one of the input/output nodes 48A while attenuating signals outside the receive portion of the first operating band between the common node 46 and the first one of the input/output nodes 48A and pass RF signals within the receive portion of the second operating band between the common node 46 and a second one of the input/output nodes 48B while attenuating signals outside the receive portion of the second operating band between the common node 46 and the second one of the input/output nodes 48B.
The secondary front end switching circuitry 38 is configured to couple a number of filters in the secondary RF filtering circuitry 40 to the secondary antenna node 42 in order to selectively route RF signals to the appropriate signal paths in the conventional RF front end circuitry 10.
While not shown, a number of LNAs may connect to the first one of the input/output nodes 48A and the second one of the input/output nodes 48B in order to amplify the receive signals therefrom for further processing.
Generally, the primary communications circuitry 12 is responsible for transmitting and receiving primary RF signals, while the secondary communications circuitry 14 is responsible for receiving secondary RF signals. As discussed herein, primary RF signals are the main transmit and receive signals used for communication, while secondary RF signals are additional signals used to improve reception quality or data throughput. For example, the secondary RF signals may be diversity receive signals or multiple-input-multiple-output (MIMO) receive signals. Further, what is referred to herein as an operating band is an RF frequency band, which may include a transmit portion (a sub-band of the RF frequency band) which is dedicated to transmitting signals and a receive portion (a sub-band of the RF frequency band) which is dedicated to receiving signals. Those skilled in the art will appreciate that some operating bands are receive-only operating bands in which the entirety of the operating band is dedicated to receiving signals. Examples of operating bands are the Long Term Evolution (LTE) operating bands.
While the conventional RF front end circuitry 10 is capable of both uplink and downlink carrier aggregation, the circuitry may suffer from signal degradation due to intermodulation distortion in certain carrier aggregation configurations. Such a problem may occur, for example, when the first operating band is LTE operating band 3 and the second operating band is LTE operating band 1. When the control circuitry 16 causes the conventional RF front end circuitry 10 to simultaneously provide RF signals within the transmit portion of the first operating band and RF signals within the transmit portion of the second operating band from the first one of the RF power amplifiers 26A and the second one of the RF power amplifiers 26B, respectively, these signals may intermodulate with one another to produce troublesome intermodulation products. Due to the combination of operating bands discussed above, intermodulation products may fall directly into the receive portion of the first operating band. The intermodulation discussed above may necessitate highly linear switching and filtering components in the conventional RF front end circuitry 10, which may be impractical when considering the design constraints thereof.
For the reasons described above, there is a need for improved RF front end circuitry capable of operating in carrier aggregation modes without excessive intermodulation.